Preserve option class in jquery select2 dropdown items

Question

Does anybody know if it possible to transfer the element class to the jquery select2 dropdown items?

<select>
  <option class="group-1"></option>
  <option class="group-1"></option>
  <option class="group-2"></option>
  <option class="group-2"></option>
</select>

I am trying to build a dynamic list based on a user's selected value from another dropdown, so if a user selects 'group 1' then I wish to only show the items with class 'group-1'. I was hoping to be able to do something like $('ul.select2 li.group-2').hide().

EDIT: I am splitting this question into 2 for clarity in the answers I have developed to solve this problem,

1. How to preserve option element classes in the select2 listing? - I am providing an answer below for those interested in this.
2. How to dynamically filter a select2 listing based on option class? I have opened a new question thread in which I am answering this question as the solutions quite different.

Answer 1

I managed to solve the question by using the templating functionality of the select2 plugin,

<script type="text/javascript">
(function( $ ) {
  'use strict';

  var opportunities = $('select#opportunities').select2({
    dropdownParent: $('#select-opportunity'),
    templateResult: formatItem
  });
  function formatItem (state) {
    if (!state.id) { return state.text; }
    var $state = $(
      '<span class="opportunity-item ' + state.element.className + '">' + state.text + '</span>'
    );
    return $state;
  }
})( jQuery );
</script>

NOTE: this does not allow you to manipulate the select2 dropdown list because the class attribute is only transfered to the inner custom <span> element of our item, and not to the actual <li> element of the dropdown select2 list. However it becomes very useful to further style the dropdown list, for example,

<style>
.opportunity-item.group-1::after{
  content: '';
   display: inline-block;
   margin-left:5px;
   width: 10px;
   height: 10px;
   -moz-border-radius: 10px;
   -webkit-border-radius: 10px;
   border-radius: 10px;
   background-color: green;
}
.opportunity-item.group-2::after{
  content: '';
   display: inline-block;
   margin-left:5px;
   width: 10px;
   height: 10px;
   -moz-border-radius: 10px;
   -webkit-border-radius: 10px;
   border-radius: 10px;
   background-color: blue;
}
</style>

resulting in,